-Example AVR Projects

Some time ago we have posted alphanumeric AVR-GCC LCD library. It works fine in 8-bit and 4-bit modes. But it has some limitations that some people may find annoying. One of them is requirement that LCD pins has to be byte aligned for instance in 8 bit mode LCD_D0 … LCD_D7 pins has to be connected to AVR single AVR port. Similar situation is with 4-bit mode where LCD data pins has to be connected to single port 4, 5, 6 and 7 pins. For both modes control pins RS, RW and E has to be connected to single port.

And this is how most LCD libraries work when you try to look for one in the internet. In reality things may be a bit different each microcontroller pin has at least several alternative functions available like ADC, INT, I2C, USART and if project requires using one or another and you still need LCD standard libraries won't work as most likely you wont be able to get all particular port pins connected to LCD. You gotta use whats left. This is why I decided to find a little time and modify LCD library to support these cases. Didn't want to write everything from scratch or change its functionality – just wanted it work with existing projects but have more freedom with new ones. So basically I left standard 8-bit and 4-bit same. The main change is adding two more modes: 8-bit mix and 4-bit mix. These modes allow connected LCD to any free pins of microcontroller.

Recently I was working on a project that involved rotary encoder. I thought I'd share some thoughts on how rotary encoder can be interfaced and programmed. Actually it is easy to work with rotary encoders - interfacing is simple – only three wires are required to connect to microcontroller (two for signal (quadrature outputs) and one for reference (GND)). When turned there is a Grey code produced on outputs that allows tracking turn speed and direction. These features allow having convenient user interface with single knob. Many rotary encoders also comes with button – so menu navigation couldn't be easier. In our project we are going to use a 12-step mechanical rotary encoder from sparkfun.

We are going to interface it to ATMega32 board with graphical LCD.

Most of AVR microcontrollers have Analog to Digital Converter (ADC) integrated in to chip. Such solution makes embedded designers life much easier when creating projects and programming them. With no need external ADC PCB takes less space, easier to create programs – it saves time and money. As an example lets take Atmega8 microcontroller which have up to 8 ADC inputs most with 10-bit resolution(excluding ADC4 and ADC5 inputs that are 8-bit). All features of AVR internal ADC can be found on official ATMEL AVR datasheets, but most important to mention are:

• ±2 LSB accuracy – so measurements aren't very accurate. If AREF voltage is 5V then error may reach ±0.04V but this is still good results for most of tasks;

• Integral nonlinearity ±0.5 LSB;

• Conversion speed up to 15kSPS at maximum resolution. This is far not enough for 20kHz audio signal sampling.

ADC unit is powered with separate power supply pins AVCC with AGND, but AVCC must not differ ±0.3V of VCC. Also ADC unit can have different voltage reference sources selectable in ADMUX register. References may be taken from AREF pin, AVCC with external capacitor or internal 2.56V voltage reference. All ADC inputs are multiplexed via multiplexer. Each channels can be selected by changing 4 bits in ADMUX register. ADC unit can operata in two modes:

This is simple demo program of reading button state, lighting LEDs, sending information via USART. 8 buttons are connected to Atmega16 port A, 8 LEDs to port B via current limiting resistors. While none of buttons arent pressed there is running light on LEDs performed, but when any of buttons is pressed then LEDs display current 8 buit counter value in binary format. Same value is sent via USART – you can see number in terminal if connected.

Standard alphanumeric LCD display controlled by 74HC164 controlled can accept 8 bit data bytes or 4 bit nibbles. Using 4 bit interface may give few benefits like you can save 4 microcontroller pins and use them for different purposes, or use small pin count Microcontrollers to control LCD like AVR ATtiny series.

When using 4 bit mode, only four data-lines of LCD (D4...D7) are used. So first is high nibble sent and then lower nibble has to be sent in order to form single byte. This way there are two cycles used to form one data or command byte. Earlier I have been using LCD library from Procyon AVRLIB, but I wasn’t satisfied with it as it generated a lots of HEX code because of many functionality included.